Smith of the California Labor Federation argued that the potential of peer pressure from colleagues pales in comparison to the influence employers can wield.

“They're not holding a paycheck over a person's head,” Smith said. “Employers are and that's a situation that's rife with the potential of harassment.”

Both sides are lobbying intensely.

This month, the U.S. Chamber of Commerce organized a “work force freedom airlift,” flooding the Capitol with business leaders from around the country urging members of Congress to reject the legislation and any compromise.

The California Labor Federation has organized a series of protests outside Feinstein's offices in the state, as well as letter-writing and e-mail campaigns.

The San Diego and Imperial Counties Labor Council is airing radio commercials lamenting the number of returning military veterans who have to settle for low-paying, nonunion jobs with no health benefits.

“Vets and their co-workers should be able to form a union at the jobs they can find – the same way they joined the military, by signing their names,” the ad says. “Senator Feinstein voted to send our soldiers to Iraq. Now she should vote for the Employee Free Choice Act.”

President Barack Obama endorsed card check during the 2008 campaign.

Labor and business don't agree about much on this issue, but they agree that Obama's position might account for Feinstein's reticence, noting that the 2007 bill had no chance with Republican George W. Bush in the White House.

“I think it's a lot easier to support something when you know you have a president who's never going to sign it. This is a much different situation,” said Lorena Gonzalez, secretary-treasurer of the San Diego and Imperial Counties Labor Council.

The chamber's Spencer agreed.

“There's a number of senators who voted for it in 2007 who have cold feet now,” Spencer said. “She's certainly not alone in that camp.”

Obama may have endorsed card check, but there have been few signs that he is doing much to move it through Congress.

“Nobody's being called to the White House,” one congressional aide said.

One labor analyst said he believes the Democratic president simply has higher priorities.

“It's not the type of thing Obama wants to waste political capital on right now because it's probably not going to go anywhere,” said Gary Chiason, a professor of industrial relations at Clark University in Worcester, Mass.

Even though Democrats took over the White House and have made significant gains in Congress, Chiason said he didn't think card check has much of a chance.

“I think the Employee Free Choice Act right now is very iffy,” Chiason said. “I think there's probably a one-out-of-three chance it will pass. It's not completely dead, but it's not very much alive because it would require a filibuster-proof majority in the Senate, and the Republicans are very much against it.”